The invention relates to improvements in plastic extrusion equipment and methods for forming film with shaped profiles on the surface where such film is eventually used in making reclosable bags or similar products.
More particularly, the invention relates to improvements in forming the profiles such that the shape can be more completely controlled at relatively high extrusion speeds so that a precise shape can be maintained to accurately and strongly interlock with another mating profile. One type of film having profiles on the surface is formed by supplying a continuous sheet of film and simultaneously extruding a profile which is laid on the film while hot so that it integrally attaches itself to the film to form a completed profile sheet. Mechanisms and processes for forming such sheets are shown in the copending applications of Takashi Noguschi, U.S. Ser. No. 178,086, filed Sept. 7, 1971 and U.S. Ser. No. 178,087, filed Sept. 7, 1971. It will be understood that the features of the invention find advantage in forming profiles by other methods and other mechanisms, but the invention will be primarily described in connection with an environment such as that shown in the above referred to copending applications, the disclosures of which are embodied herein by reference. The features described herein may be employed, for example, in an extrusion arrangement wherein the profile is not formed separately and applied to a film white hot, but wherein the profile and film are extruded simultaneously out of a single die opening. It is also contemplated that the features of the invention may be employed in an arrangement wherein the film and profile are extruded separately, but substantially immediately joined to each other.
In the formation of profile sheets with the improvement of extrusion techniques and profile and film designs, it has become possible to form a very thin film of only a few mils of thickness and to make the profile very small and yet obtain interlocking profiles which will join to each other with a strength that approaches or surpasses the strength of the film. To obtain an efficient highly effective interlocking profile depends upon the accuracy thereof, and this accuracy is hard to maintain at high extrusion speeds. It has been discovered that an important factor in maintaining the shape of the profile is in controlling the cooling thereof.
It is accordingly an object of the present invention to provide an improved mechanism and method for the production of profiled film obtaining more accurate and better control of profile shape and/or higher extrusion rates.
A still further object of the invention is to provide an improved method and mechanism for accurately controlling the shape of extruded plastic profiles during continuous extrusion.
Other objects, advantages and features, as well as equivalent mechanisms and methods which are intended to be covered herein, will become more apparent with the disclosure of the preferred embodiments in the specification, claims and drawings, in which: